Methods and devices for an lambda regulation in internal combustion engines are used to reduce the emission of damaging exhaust gases into the environment if the at least one catalytic converter is arranged in the exhaust system of the internal combustion engine. In order to maintain a 3-way catalytic converter in an optimal operating state it is necessary to control the fuel-mixture generation of the internal combustion engine using an lambda control such that at least a mean lambda ratio develops as closely as possible approximating 1.0. Here, it is known to provide a front lambda control circuit with a front oxygen sensor, arranged downstream in reference to the internal combustion engine and upstream in reference to the catalytic converter, and a rear lambda control circuit with at least one rear oxygen sensor, arranged downstream in reference to the catalytic converter. It is disadvantageous that such systems react somewhat slowly so that undesired emissions bursts can occur, in which the catalytic converter is briefly outside the optimal operating state. Therefore it has been attempted to optimize the quality of the control by improving the processing of the signals from the sensors. The publications DE 102 25 937 A1, DE 196 06 652 A1, and DE 103 39 063 A1 show such systems, for example.
It is possible to detect the behavior of the catalytic converter or to model it such that an intervention occurs already before the rear sensor detects any deviation from the target value. In particular, it can be beneficial to use a catalytic converter model for detecting presently stored oxygen amounts because the oxygen stored in the catalytic converter largely influences the conversion of contaminants and the reaction of the sensor signal. Information concerning the present oxygen status of the catalytic converter can be used in different ways for improving the lambda control. This includes the modification or amendment of control algorithms. From the publication DE 102 46 505 A1 a method is known for heating catalytic converters by alternating charges with sub- and super-stoichiometric exhaust gas. Here, a limit is set for the present oxygen storage capacity of the catalytic converter which is modeled by age and temperature or which can be determined by experimentally forced bursts. The flow of exhaust gas is multiplied by the respective relative oxygen surplus or oxygen demand and the product is integrated over time. When the limit is reached the phase is changed.
One problematic disadvantage of this approach is the fact that the present oxygen status of the catalytic converter must be determined very precisely and furthermore a precise description of the correlation between the oxygen status and the conversion performance of the catalytic converter is necessary when the lambda control shall be improved, because otherwise any deviation from the model behavior results in an insufficient reaction of the regulator. It is understood that it is also possible to determine which time is to be assumed at which the model of the oxygen storage capacity of the catalytic converter no longer sufficiently describes the real behavior and at which the information of the present oxygen state of the catalytic converter is waived. In this case the lambda control must be performed in a conventional manner entirely based on the signal of the oxygen sensors.